Recently, high energy lithium-ion cells have been constructed which include alloy electrochemically active materials in the negative electrode. Such materials typically have higher gravimetric and volumetric energy density than graphite alone. Alloy anode materials are typically Si or Sn-based and comprise an electrochemically active component and an electrochemically inactive component. The electrochemically inactive component limits the volume expansion of the particles. For example, Si can expand by 280% when fully lithiated (2194 mAh/cc capacity), whereas a Si/electrochemically inactive 40/60 two-component alloy will have about 112% volume expansion (1573 Ah/L capacity). This effect is a simple dilution. The total capacity is reduced linearly with the addition of an electrochemically inactive component. An undesirable property of alloy anode materials is that they can catalyze electrochemical reduction at low voltages.
Alloy anode materials are usually amorphous or nanocrystalline to improve cycling performance. Such microstructures are typically made by meltspinning, mechanical milling, or sputtering. Of these, melt spinning and mechanical milling are the most commercially viable.
There is a need for alloy anode materials that resist volumetric expansion and have high volumetric and gravimetric energy density. There is also a need for alloy anode materials that have relatively low surface area and less surface reactivity than conventional materials.